No such thing, and likely never will be. Anything that can't be done with existing rimfire rounds is already overlapped by small centerfire rounds. There is no need to try and re-invent the wheel when the wheel already works fine as is.
Better magazine design, such as the Archangel Marauder (Nomad?) magazines, as well as number of others, have already found solutions to unattractive banana magazines. Introducing small moving parts into the breech is a recipe for many failures. Such an endeavor simply would not be economical, unless you have unlimited resources to pursue it.